Communication between user equipment (Device-to-Device, “D2D” for short) means that user equipment directly communicate with each other. A proximity service between user equipment (Device to Device Proximity Service, “D2D ProSe” for short) has become a research topic in a system of Rel.12 in a Long Term Evolution (Long Term Evolution, “LTE” for short) system in the 3rd Generation Partnership Project (3rd Generation Partnership Project, “3GPP” for short), and support of the D2D communication starts from the system of Rel.12.
During a research on the D2D ProSe, both sending and detection of a discovery signal are periodically performed on a resource reserved by a system. For example, user equipment A periodically sends a discovery signal on a resource reserved by the system, and user equipment B periodically detects a discovery signal on a resource reserved by the system. To ensure a coverage area of a discovery signal, the user equipment A generally sends the discovery signal by using maximum power. To ensure that the user equipment B can quickly discover the user equipment A, the user equipment A needs to send a discovery signal in a short period. For example, when a period of sending a discovery signal is 2.56 seconds, the user equipment B discovers the user equipment A within a maximum of 2.56 seconds. However, sending a discovery signal in a short period by the user equipment A greatly increases energy consumed by the user equipment A. To reduce the energy consumed by the user equipment A when the user equipment A sends a discovery signal to the user equipment B, the user equipment A may send the discovery signal in a long period. For example, a period of sending a discovery signal is 600 seconds. However, consequently, it may take an extremely long time for the user equipment B to discover the user equipment A.
In conclusion, user equipment periodically sends a discovery signal on a resource reserved by a system, which leads to a conflict between efficiency in detecting the discovery signal and energy consumed by the user equipment. Either the energy consumed by the user equipment is extremely high, or it takes an extremely long time to detect the discovery signal.
Therefore, the present invention proposes a discovery signal transmission method to balance efficiency in detecting a discovery signal and energy consumed by the user equipment to send the discovery signal.